The invention furthermore relates to a device for recognizing a derailment state of a wheel of a rail vehicle, which displays at least one acceleration sensor for the acquisition of the acceleration of the wheel perpendicularly to a rail plane, where the acceleration sensor is fitted out with an analysis unit for the analysis of an acceleration signal generated by the acceleration sensor.
A wheel or wheel set of a rail vehicle, for example, can be subjected to quasistatic accelerations caused by the terrain profile, but also by accelerations caused by derailments. However, with regard to the detection of a derailment, it is only the accelerations that are caused by the movement of the wheel set perpendicularly to the rail plane that are of interest here. In the following, accelerations that work upon the wheel sets perpendicularly to the rail plane will be referred to as fall accelerations. In that sense, the vertical speeds, resulting from these accelerations, will in this document also be referred to as fall speeds.
Such fall speeds can be caused, in case of a derailment, by the ground acceleration and by the primary spring that is being released, whereby the terminal point of this “fall movement” of the wheel or the wheel set is usually determined by a fixed roadway.
Sensors that can measure the proportion of acceleration are not sturdy enough for use on rail vehicles. Sturdy sensors, however, cannot measure the proportion; they have a lower boundary frequency. Slow changes in acceleration thus cannot be acquired. Furthermore, the measurement signals usually display an offset that is subjected to drift phenomena. When one uses sturdy acceleration sensors, it is not the quasistatic parts of the acceleration of the wheel set, but rather primarily drift phenomena and low-frequency electromagnetic inputs that result in the amplitude curve of the generated acceleration signals.
German Patent No. DE 199 53 677 C1 discloses a method of the kind mentioned above. The known document describes a method for recognizing a derailment of a track-bound vehicle. For this purpose, an acceleration of a structural element of the track-bound vehicle, which element is directly or indirectly in contact with the track, is determined vertically and/or laterally with respect to a direction of movement. The acceleration signal is integrated doubly over the time and this doubly integrated acceleration signal is compared to an upper and/or lower boundary value, whereby a derailment has taken place when the boundary value is either exceeded or not attained.
There is one disadvantage connected with this known embodiment in that the double integration brings about a very poor signal-to-noise ratio. For instance, a simple integration can reduce the signal-to-noise ratio by 20 dB per decade of the signal that is to be integrated. A double integration will reduce the signal-to-noise ratio already by 40 dB per decade. Thus, in case of a double integration, a low-frequency jamming signal is amplified by a factor of 10 (20 dB) more than the actual useful signal—the fall acceleration. Stiff requirements are established for the analysis electronics by double integration, as a result of which, the production costs can turn out to be high. Furthermore, using the known method or system, there can be delays in the recognition of derailed states due to the required expensive analysis electronics.
It is therefore the object of the invention to provide a way that makes it possible in a simple, reasonably priced and fast manner to recognize a derailment of a wheel set with a high degree of reliability.